Nuclear Strikes on Iran:

What We Don't Know

June 24, 2025

On June 21, the United States struck three nuclear sites in Iran in an operation designed to “severely degrade Iran’s nuclear weapons infrastructure,” according to General Dan Cain, the Chairman of the Joint Chiefs of Staff. Secretary of Defense Pete Hegseth went further, claiming that “Iran’s nuclear ambitions have been obliterated.”

A number of officials, however, have warned that it is still too early to know how much damage was actually inflicted and to know how much material and equipment may have been removed from the nuclear sites before they were attacked. This uncertainty poses an important question: has the military campaign pushed the threat of an Iranian bomb far into the future, or has the campaign left enough potential behind to trigger a race to the bomb within the next year or so. The answer will determine whether the strikes are judged a success.

1. What happened to Iran’s stockpile of enriched uranium? 

Iran had 408.6 kg of uranium enriched to 60% of the fissionable U-235 isotope as of late May, according to the International Atomic Energy Agency (IAEA). Agency inspectors last saw the stockpile on June 10. This level of enrichment has no plausible civilian application. It is nearly weapons-grade and Iran’s stockpile would be sufficient to fuel up to ten nuclear weapons, with further enrichment. The IAEA warned that Iran is “the only non-nuclear-weapon State in the world that is producing and accumulating uranium enriched to 60%” and that this production is “a matter of serious concern.”

The location of this 60% material is now uncertain. Iran had principally been producing it at the Fordow enrichment plant, which was struck by the United States on June 21. A smaller amount of 60% material had been produced at the above-ground enrichment plant at Natanz, which was destroyed by Israel on June 13. Some of this accumulated material may have been at these production locations. Much of the stockpile was believed to be stored in tunnels at Esfahan, a large nuclear research and development complex. Entrances to these tunnels appear to have been struck by the United States.

U.S. officials have claimed that the 60% material had not been moved and that U.S. strikes targeted locations where the material was still being stored. Vice President J.D. Vance said on June 23 that the uranium was buried as a result of the U.S. strikes. However, Iran informed the IAEA on June 13, on the first day of Israel’s bombing campaign, that it would “adopt special measures to protect our nuclear equipment and materials”. IAEA Director General Rafael Grossi subsequently said he took this to mean that Iran planned to move the material in order to protect it.

This material could be enriched to weapons grade in a matter of weeks and processed further in a few more weeks to fuel an implosion weapon that would fit on a missile. Such a weapon would have to be tested. Alternatively, Iran could further process its 60% material and use it in a less sophisticated “gun type” nuclear weapon such as the one dropped on Hiroshima, which would not have to be tested. Iran has enough material for one or more such devices, but they would be heavier and larger than an implosion device.

In addition to the fate of the 60% material, which has garnered much attention, Iran also had 275 kg of 20% enriched uranium and 5,509 kg of 5% enriched uranium as of late May. The availability of this material has nuclear weapon implications. Twenty percent enriched uranium is approximately 90% of the way to weapon-grade and Iran’s stockpile would be sufficient to fuel at least two implosion weapons. The 5% stockpile would be sufficient to fuel at least 10 implosion weapons but would require more enrichment work to reach this level. The location and status of these stockpiles has not been addressed publicly.

2. Can Iran still enrich uranium? 

Iran has three known gas centrifuge uranium enrichment facilities: a deeply buried plant at Fordow (located beneath a mountain) that houses approximately 2,700 centrifuges, an underground plant at Natanz that houses some 17,000 centrifuges, and a pilot plant at Natanz, portions of which are located above and below ground, that houses about 1,700 centrifuges. All three appear to have been damaged or destroyed.

The Fordow plant was first struck by the United States on June 21, using 12 bunker-busting bombs. Israel subsequently struck roads leading to Fordow in order to disrupt access to the site. It is impossible to fully assess the damage at Fordow, but the IAEA Director General has stated that “Given the explosive payload utilized, and the extreme vibration-sensitive nature of centrifuges, very significant damage is expected to have occurred.”

Israel destroyed the above ground Natanz plant in its initial strikes on June 13, along with electricity infrastructure that may have caused broader damage to centrifuges operating in underground locations, according to the IAEA. The United States also used ground-penetrating munitions to strike the underground centrifuge halls at Natanz on June 21, causing further damage to this facility.

It is unclear whether Iran was able to remove centrifuges or other equipment from these facilities before they were struck. Installed or operating centrifuges are connected together and secured to the floor and would not be quick to remove.

Iran is known to make and store centrifuge components at other locations, which have not been monitored by the IAEA since February 2021. Some of these sites have been struck by Israel since June 13 (at Esfahan, the Tehran Nuclear Research Center, and Karaj) but Iran may have removed its equipment beforehand. The remaining centrifuges might be sufficient to set up a small enrichment plant. Or Iran may be manufacturing centrifuge components (or storing them) at additional locations, unknown to the IAEA and not struck by Israel.

Iran also announced on June 12, the day before Israeli strikes began, that it was building a fourth uranium enrichment plant, reportedly deeply buried. The IAEA said the plant was located within the Esfahan complex.

3. Does Iran have secret facilities for uranium work?

The nuclear complex at Esfahan houses a number of plants critical to producing nuclear weapons fuel, notably a plant to convert enriched uranium gas to metal, which would allow for the production of weapon components. Israeli strikes on June 13 damaged this plant. Without an alternative plant to conduct this work, Iran would be unable to produce nuclear weapons components.

However, Iran could already have such a plant, or if not, could construct one. Only dual-use industrial equipment is needed to convert the uranium in the gas to metallic form, and then to cast and machine the metal into weapon components. The process could be done on a laboratory scale and would be difficult to detect.

If Iran’s stockpile of enriched uranium is not available, Iran would need a plant to convert natural uranium ore to the gas that is enriched in centrifuges. Israel damaged the primary chemical laboratory and uranium conversion plant at Esfahan on June 13 and U.S. strikes hit buildings “related to the uranium conversion process” on June 21, according to the IAEA.

4. What are the long-term risks of military strikes?

Israeli and U.S. air strikes may push Iran to pursue a crash program to develop nuclear weapons, since the threshold nuclear program Iran had achieved was not sufficient to deter the strikes. In addition, Iran’s other deterrent, which consisted of missile attacks by itself or its proxies, has been virtually eliminated. These developments may convince Iran that it needs nuclear weapons as a more reliable deterrent.

A second risk is loss of public knowledge of Iran’s nuclear program. Before the strikes, Agency inspectors had continued to verify Iran’s enriched uranium and the locations where it was being produced. Such access has been suspended as a result of the military strikes. In the aftermath of the strikes, Iran may reduce or terminate its cooperation with the IAEA. Iran may also decide to withdraw from the Nuclear Nonproliferation Treaty, which provides the legal basis for the IAEA’s access to nuclear sites in Iran.

Iran has been building its nuclear program for decades. The program has advanced despite a decades-long effort to stop it diplomatically and an equally lengthy campaign of sanctions and sabotage. Have Israeli and U.S. air strikes now succeeded in seriously setting back Iran’s nuclear weapons bid or rather accelerated Iran’s race to the bomb?

Iran Watch is a website published by the Wisconsin Project on Nuclear Arms Control. The Wisconsin Project is a non-profit, non-partisan organization that conducts research, advocacy, and public education aimed at inhibiting strategic trade from contributing to the proliferation of weapons of mass destruction. 

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